1. Technical Field
The present invention relates to a finishing technique for optical fibers and, more particularly, to tapering and metallization techniques for optical fibers including a lensed endface.
2. Description of the Prior Art
For most optical communication applications, it is necessary to align and fix the position of an optical fiber with respect to a transmitting or receiving device. In general, optical fibers are often processed to include a metallic outer coating such that the metal may be soldered to a fixed reference plane and facilitate alignment. The metallic coating may further allow for a fiber to be hermetically sealed to the optical device package. One such arrangement for providing both alignment and hermeticity is disclosed in U.S. Pat. No. 4,119,363 is issued to I. Camlibel et al. on Oct. 10, 1978. In the Camlibel et al. arrangement, a bare optical fiber is centered through a metal tube disposed within a package wall and a cylindrical, narrow bore solder preform is disposed within the tube. The preform is heated to a molten state and the fiber is adjusted within the molten solder to achieve optimum coupling to the laser. The solder, upon solidifying and cooling, squeezes against the fiber and forms a hermetic seal. The Camlibel et al. arrangement, however, may result in some misalignment of the fiber during the cooling process. Further, the package cannot thereafter be exposed to elevated temperatures which may soften the solder and allow the fiber to move.
In order to increase the coupling between an optical device and fiber, a lens may be inserted in the optical path between the device and the fiber. The lens may either comprise a discrete element which must be aligned to both the device and the fiber, or a device which is attached directly to the endface of the fiber. When utilizing a fiber including a metallic coating, problems may exist with the latter arrangement where the presence of the metal may interfere with the integrity of the attachment. U.S. Pat. No. 4,622,055 issued to K. Mathyssek et al. on Nov. 11, 1986 discloses a method for removing a metallic coating from the fiber tip area such that a lens may be epoxied onto the endface of a bare glass fiber. In particular, the fiber is passed through an arc or flame where it is softened to the point that the glass constricts and separates from the metallic coating. The fiber is then drawn and cleaved such that an endface is formed which is free of the metallic coating. A lens may then be attached to the cleaved endface. A problem may arise, however, in controlling the attachment of the lens to the fiber tip, which can result in increasing the time and expense involved in forming such a lensed fiber.
In contrast to the process of attaching a lens to the fiber endface, there exist various wet chemical etching techniques for forming an integral lens directly on the fiber endface. By controlling various etching parameters, for example, the fiber cladding may be removed such that the core region remains exposed. Other techniques exist for preferentially etching the cladding with respect to the central core region. However, there have arisen problems in both tapering a lensed fiber and applying a metallic coating to such fibers including an integral lens, since these processes have been found to affect the properties of such an integral lens.
Therefore, a need remains in the prior art for a method of finishing an optical fiber which does not alter the property of an integral lens formed on the endface thereof.